Molded article of composite resin containing fibers

ABSTRACT

A molded article of a composite resin containing fibers includes a base resin 1 and a fibrous filler 2 having fibrillated ends in a fiber length direction. An expression Ho × 0.4 ≤ H ≤ Ho is satisfied where H is a maximum height for an unbroken first plate-like test piece having a thickness of 1 to 2 mm after the test piece is kept at -10° C. for three hours and then is hit by a dropped weight of 250 g; and Ho is as same maximum height for the unbroken second plate-like test piece only made of the base resin with a thickness of 1 to 2 mm as for the first plate-like test piece. An expression So × 0.4 ≤ s ≤ So is satisfied where S is a Charpy impact strength (JIS K 7111) of the molded article, and So is a Charpy impact strength of the molded article only made of the base resin.

FIELD OF THE INVENTION

The present invention relates to a molded article of a composite resincontaining a fibrous filler.

BACKGROUND OF THE INVENTION

So-called “general purpose plastics” such as polyethylene (PE),polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) arequite inexpensive and are easily molded with a light weight that is ahalf or less those of metals or ceramics. Thus, general purpose plasticsare widely used as materials for various daily necessaries such as bags,packages, containers, and sheets, industrial components such asautomobile parts and electrical components, articles for daily use, andsundry goods.

Unfortunately, general purpose plastics have insufficient mechanicalstrength and thus do not have satisfactory characteristics required formaterials used for machine products of automobiles and variousindustrial products including electric, electronic, and informationproducts. The applicability of general purpose plastics is limited underpresent circumstances.

In contrast, so-called “engineering plastics” such as polycarbonate,fluorocarbon resin, acrylic resin, and polyamide have excellentmechanical characteristics and are used for machine products ofautomobiles and various industrial products including electric,electronic, and information products. However, engineering plastics areexpensive and are difficult to use in a monomer recycle,disadvantageously resulting in a large environmental load.

Thus, it is desired to considerably improve the material characteristics(including mechanical strength) of general purpose plastics. In order toreinforce general purpose plastics in a known technique, for example,natural fibers as a fibrous filler, glass fibers, and carbon fibers aredispersed into resin of general purpose plastics, thereby improving themechanical strength of the general purpose plastics. An organic fibrousfiller containing cellulose is, in particular, inexpensive and isdisposed of in an environmentally friendly manner. Thus, such an organicfibrous filler has received attention as reinforcing fibers.

Various manufacturers have conducted studies to improve the mechanicalstrength of general purpose plastics. In JP5577176B, cellulose fibershaving a maximum fiber diameter of 100 nm or less and an aspect ratio ofat least 2000 are added to general purpose plastics so as to increasethe modulus of elasticity and dimensional stability of the generalpurpose plastics.

In the technique of JP5577176B, however, if fibers are added with amaximum fiber diameter of 100 nm or less and an aspect ratio of at least2000, that is, the ratio of a fiber length to a fiber diameter, afibrous filler tends to be oriented in the flowing direction of moltenbase resin that is injected during molding. Thus, the impact strength(e.g., a Charpy impact strength) of an impact in one direction can beincreased to a certain degree but in a direction orthogonal to theflowing direction, an impact strength, in particular, a surface impactstrength (e.g., weight-dropping impact strength) may decrease.

DISCLOSURE OF THE INVENTION

A molded article of a composite resin containing fibers according to thepresent invention has been devised to solve the problem. An object ofthe present invention is to obtain a molded article with high modulus ofelasticity and high resistance to surface impact strength and impactstrength in one direction.

In order to attain the object, a molded article of a composite resincontaining a fibrous filler in base resin according to the presentinvention is provided, wherein the fibrous filler has a fibrillated parton each end of the fibrous filler in a fiber length direction,

-   the composite resin exhibits physical characteristics satisfying:-   Ho× 0.4 ≤ H ≤ Ho-   where H is a maximum height when a first plate-like test piece is    not broken when a weight of 250 g is dropped from a certain height    after the first plate-like test piece is kept at -10° C. for three    hours, the first plate-like test piece being made of the composite    resin with a thickness of 1 to 2 mm; and Ho is a maximum height when    a second plate-like test piece is not broken when a weight of 250 g    is dropped from a certain height after the second plate-like test    piece is kept at -10° C. for three hours, the second plate-like test    piece being only made of the base resin with the same thickness as    the first plate-like test piece, and-   So× 0.4 ≤ S ≤ So-   where S is a Charpy impact strength specified for JIS K 7111 of the    molded article of the composite resin, and So is a Charpy impact    strength specified for JIS K 7111 of the molded article only made of    the base resin.

Another molded article of the composite resin containing the fibrousfiller in the base resin according to the present invention is provided,wherein the fibrous filler has a non-fibrillated part that is notfibrillated and a fibrillated part on each end of the fibrous filler ina fiber length direction.

Preferably, the fibrous filler has a median fiber diameter of 0.1 to 2µm on the fibrillated part, and the fibrous filler has a median fiberdiameter of 5 to 30 µm on the non-fibrillated part.

Preferably, the fibrous filler is natural fibers of cellulose.

Preferably, the base resin is an olefin resin.

Still another molded article of the composite resin containing thefibrous filler in the base resin according to the present invention isprovided, wherein the fibrous filler has a fibrillated part on each endof the fibrous filler in a fiber length direction,

-   the fibrous filler has a median fiber diameter of 0.1 to 2 µm on the    fibrillated part and has a median fiber diameter of 5 to 30 µm on    the non-fibrillated part,-   the fibrillated part prevents cracking caused by connection of a    plurality of crazing defects occurring when an impact force is    applied to the molded article in a plane direction, and-   the non-fibrillated part that is not fibrillated prevents cracking    defects occurring when an impact force is applied to the molded    article in one direction as in a Charpy impact test.

According to the present invention, the molded article of the compositeresin is prepared by mixing the fibrous filler in the base resin, thefibrous filler having a fibrillated part on each end of the fibrousfiller in the fiber length direction, the composite resin exhibitingphysical characteristics satisfying Ho × 0.4 ≤ H ≤ Ho and So × 0.4 ≤ S ≤So. This can obtain a high modulus of elasticity and high resistance toan impact in the plane direction and an impact in one direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view showing a molded article ofa composite resin according to an embodiment of the present invention;

FIG. 1B is a schematic cross-sectional view showing that an impact isapplied to the molded article in a plane direction;

FIG. 1C is a schematic cross-sectional view showing that an impact isapplied to the molded article in one direction;

FIG. 2A is a first schematic cross-sectional view for explaining theinfluence of a difference in the dispersion state of a fibrous filler;

FIG. 2B is a schematic cross-sectional view for explaining the influenceof an impact applied to the molded article of FIG. 2A in the planedirection;

FIG. 2C is a schematic cross-sectional view for explaining the influenceof an impact applied to the molded article of FIG. 2A in one direction;

FIG. 3A is a second schematic cross-sectional view for explaining theinfluence of a difference in the dispersion state of the fibrous filler;

FIG. 3B is a schematic cross-sectional view for explaining the influenceof an impact applied to the molded article of FIG. 3A in the planedirection;

FIG. 3C is a schematic cross-sectional view for explaining the influenceof an impact applied to the molded article of FIG. 3A in one direction;and

FIG. 4 is a flowchart for explaining the manufacturing process of themolded article of the composite resin according to the embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENT

A molded article of a composite resin containing fibers according to thepresent invention will be described below with reference to theaccompanying drawings.

The molded article of the composite resin containing fibers according toan embodiment of the present invention is made of the composite resinobtained from a molten mixture containing a base resin, a fibrousfiller, and a dispersant as needed. As shown in the schematiccross-sectional view of FIG. 1A, the molded article of the compositeresin containing fibers includes a base resin 1 containing a dispersedfibrous filler 2. The fibrous filler 2 is carbonized in a specificratio.

In order to ensure high moldability, a thermoplastic resin is preferablyused as the base resin 1. The thermoplastic resin is, for example, anolefin resin (including a cyclic olefin resin), a styrene resin, a(meta)acrylic resin, an organic acid vinyl ester resin or a derivativethereof, a vinyl ether resin, a halogen-containing resin, apolycarbonate resin, a polyester resin, a polyamide resin, athermoplastic polyurethane resin, a polysulfone resin (e.g., polyethersulfone or polysulfone), a polyphenylene ether resin (e.g., 2,6-xylenolpolymer), a cellulose derivative (e.g., cellulose esters, cellulosecarbamates, or cellulose ethers), a silicone resin (e.g.,polydimethylsiloxane or polymethylphenyl siloxane), or rubber or anelastomer (e.g., diene rubbers of polybutadiene or polyisoprene, astyrene-butadiene copolymer, an acrylonitrile-butadiene copolymer,acrylic rubber, urethane rubber, or silicone rubber). One of the resinsmay be used or two or more of the resins may be used in combination. Thebase resin 1 is not limited to these materials as long asthermoplasticity is provided.

Of these thermoplastic resins, the base resin 1 is preferably an olefinresin having a relatively low melting point. Olefin resins include acopolymer of olefin monomers and a copolymer of olefin monomers andother copolymerizable monomers in addition to a monopolymer of an olefinmonomer. Olefin monomers include, for example, chain olefins (α-C2-20olefins such as ethylene, propylene, 1-butene, isobutene, 1-pentene,4-methyl-1-pentene, and 1-octene) and cyclic olefins.

One of the olefin monomers may be used or two or more of the olefinmonomers may be used in combination.

Of the olefin monomers, chain olefins such as ethylene and propylene arepreferable. Other copolymerizable monomers include, for example, fattyacid vinyl esters such as vinyl acetate and vinyl propionate;(meta)acrylic monomers such as (meta)acrylic acid, alkyl (meta)acrylate,and glycidyl (meta)acrylate; unsaturated dicarboxylic acids or anhydridethereof such as maleic acid, fumaric acid, and maleic anhydride; a vinylester of carboxylic acid (e.g., vinyl acetate or vinyl propionate);cyclic olefins such as norbornene and cyclopentadiene; and dienes suchas butadiene and isoprene. One of the copolymerizable monomers may beused or two or more of the copolymerizable monomers may be used incombination. Specific examples of olefin resins include copolymers ofchain olefins (particularly α-C2-4 olefin) including polyethylene (e.g.,a low density, medium density, high density or linear low-densitypolyethylene), polypropylene, an ethylene-propylene copolymer, and aterpolymer such as ethylene-propylene-butene-1.

The dispersant will be discussed below.

The composite resin preferably contains the dispersant in order toimprove adhesion between the fibrous filler 2 and the base resin 1 orthe dispersion of the fibrous filler 2 in the base resin 1. Thedispersant may be a titanate coupling agent; a silane coupling agent;modified polyolefin prepared by grafting of unsaturated carboxylic acid,maleic acid, or maleic anhydride; fatty acid; a fatty acid metal salt;or fatty ester. The silane coupling agent is preferably an unsaturatedhydrocarbon agent or an epoxy agent. The surface of the dispersant maybe denatured with thermosetting or thermoplastic polymer components. Inthe present embodiment, if the dispersant is contained in the moldedarticle of the composite resin containing fibers, the content of thedispersant is preferably 0.01 to 20 mass%, is more preferably 0.1 to 10mass%, and is most preferably 0.5 to 5 mass%.

If the content of the dispersant is less than 0.01 mass%, faultydispersion may occur. If the content of the dispersant exceeds 20 mass%,the strength of the molded article of the composite resin containingfibers may decrease. The dispersant is properly selected by acombination of the base resin 1 and the fibrous filler 2. The dispersantdoes not need to be added if the dispersant is unnecessary for acombination.

The fibrous filler 2 will be discussed below.

The fibrous filler 2 is used to mainly improve mechanicalcharacteristics and dimensional stability with a reduction in thecoefficient of linear expansion. For this purpose, the fibrous filler 2preferably has a higher modulus of elasticity than the base resin 1.Specific examples of the fibrous filler 2 include pulp; cellulosenanofibers; lignocellulose; lignocellulose nanofibers; natural fiberssuch as cotton, silk, wool, jute fibers, and hemp; regenerated fiberssuch as rayon and cupra; semi-synthetic fibers such as acetate andpromix; synthetic fibers such as polyester, polyacrylonitrile,polyamide, aramid, and polyolefin; carbon fibers; a carbon nanotube; andmodified fibers whose surfaces and ends are chemically modified. Ofthese examples, natural fibers of cellulose are particularly preferablein view of availability, a high modulus of elasticity, a low coefficientof linear expansion, and environmental friendliness.

The content of the fibrous filler 2 is preferably 1 to 80 mass%, morepreferably 5 to 70 mass%. If the content of the fibrous filler 2 is lessthan 1 mass%, it is difficult to ensure the mechanical strength of themolded article of the composite resin containing fibers. If the contentof the fibrous filler 2 exceeds 80 mass%, melting viscosity increasesduring melting, dispersion, and kneading and during injection molding.This tends to reduce the dispersion of the fibrous filler 2 in the baseresin 1 and cause a poor appearance on the obtained molded article ofthe composite resin containing fibers.

As shown in FIG. 1A, the fibrous filler 2 has a fibrillated part 3 thatis at least partially fibrillated on each end of a fiber in the fiberlength direction. The fibrous filler 2 has a non-fibrillated part 4 thatis not fibrillated at the center of the fiber in the fiber lengthdirection.

FIGS. 2A and 3A show comparative examples.

FIG. 2A shows that the fibrous filler 2 is not sufficiently fibrillatedwith the non-fibrillated part 4 having a large fiber diameter in theabsence of a fibrillated part. FIG. 3A shows that the fibrous filler 2is considerably fibrillated. The non-fibrillated parts are not clearlyfound and only the fibrillated parts 3 are dispersed in the form ofshort fibers.

As for an optimum state of the fibrous filler 2, experiments andsimulation results made by the present inventors prove that thefibrillated part 3 preferably has a median fiber diameter of 0.1 to 2 µmand the non-fibrillated part 4 preferably has a median fiber diameter of5 to 30 µm.

FIGS. 1B, 2B, and 3B are schematic cross-sectional views showing that animpact, e.g., a weight drop impact is applied in a plane direction indifferent dispersion states of the fibrous filler 2. Reference numeral 5denotes an impact force applied in the plane direction. Referencenumeral 6 denotes crazing defects caused by the surface impact force 5on the fibrillated parts 3 (FIGS. 1B and 3B) or the ends of thenon-fibrillated parts 4 (FIG. 2B).

In FIG. 1B showing the present embodiment, the crazing defects 6 appearin quite small sizes, particularly in the case where the fibrillatedpart 3 has a median fiber diameter of 0.1 to 2 µm. Thus, the crazingdefects 6 are hardly connected into large crazing defects. Furthermore,the effect of dispersing the propagation of an impact force reduces theoccurrence of cracking from the crazing defects 6.

In contrast, if the fibrillated parts 3 are not clearly found as shownin the comparative example of FIG. 2B, the multiple large crazingdefects 6 occur near the fibers of the non-fibrillated parts 4 and arelikely to be connected to one another. This increases the occurrence ofcracking from the crazing defects 6. According to this phenomenon, evenif the median fiber diameter of the fibrillated part 3 is smaller than0.1 µm, the large crazing defects 6 are likely to occur near thenon-fibrillated parts 4 instead of the ends of the fibrillated parts 3.If the median fiber diameter of the fibrillated part 3 is larger than 2µm, the effect of suppressing the expansion of the crazing defects 6 bythe fibrillated parts 3 is hardly exerted. This may increase theoccurrence of cracking from the crazing defects 6.

In the comparative example of FIG. 3B, the crazing defects 6 are quitesmall in size as in FIG. 1B. However, this configuration increases theprobability of uniform dispersion or gathering of the crazing defects 6,thereby connecting the crazing defects 6 so as to increase theoccurrence of cracking from the crazing defects 6.

FIGS. 1C, 2C, and 3C are schematic cross-sectional views showingdifferent behaviors in different dispersion states of the fibrous filler2 when a large impact is applied in one direction as in a Charpy impacttest (JIS K7111). Reference numeral 7 denotes an impact force applied inone direction. Reference numeral 8 denotes a cracking defect caused bythe one-direction impact force 7.

In FIG. 1C showing the present embodiment, the one-direction impactforce 7 can be reduced by the non-fibrillated parts 4 so as toconsiderably suppress the expansion of the cracking defects 8,particularly in the case where the non-fibrillated part 4 has a medianfiber diameter of 5 to 30 µm.

As shown in the comparative example of FIG. 2C, even if the fibrillatedparts 3 are not clearly found, the expansion of the cracking defects 8can be considerably suppressed by the same effect as long as thenon-fibrillated parts 4 have sufficiently large diameters.

If the non-fibrillated parts 4 are not clearly found as shown in thecomparative example of FIG. 3C, fibers are cut by the impact of theone-direction impact force 7, particularly in the case where the medianfiber diameter of the fibrillated part 3 is smaller than 5 µm. Thus, theimpact cannot be reduced and the expansion of the cracking defects 8cannot be suppressed, thereby increasing the occurrence of cracking.Conversely, if the median fiber diameter of the non-fibrillated part 4exceeds 30 µm, the large crazing defects 6 are likely to occur near thenon-fibrillated parts 4 upon the molding of the molded article.Moreover, the crazing defects 6 are likely to be connected to oneanother both in the plane direction and one direction. This increasesthe occurrence of cracking from the crazing defects 6.

In order to improve adhesion with the base resin 1 or dispersion in themolded article, the fibrous filler 2 may be surface-treated with, forexample, a titanate coupling agent; a silane coupling agent; modifiedpolyolefin prepared by grafting of unsaturated carboxylic acid, maleicacid, or maleic anhydride; fatty acid; a fatty acid metal salt; or fattyester. Alternatively, the fibrous filler 2 may be surface-treated withthermosetting or thermoplastic polymer components.

The physical characteristics of the composite resin need to satisfy Ho ×0.4 ≤ H ≤ Ho where H is a maximum height when a first plate-like testpiece is not broken when a weight of 250 g is dropped from a certainheight after the first plate-like test piece is kept at -10° C. forthree hours, the first plate-like test piece being made of the compositeresin with a thickness of 1 to 2 mm; and Ho is a maximum height when asecond plate-like test piece is not broken when a weight of 250 g isdropped from a certain height after the second plate-like test piece iskept at -10° C. for three hours, the second plate-like test piece beingonly made of the base resin with the same thickness as the firstplate-like test piece. Furthermore, the physical characteristics of thecomposite resin need to satisfy So × 0.4 ≤ S ≤ So where S is a Charpyimpact strength specified for JIS K 7111 of the molded article of thecomposite resin, and So is a Charpy impact strength specified for JIS K7111 of the molded article only made of the base resin.

This can achieve a high modulus of elasticity and high resistance to animpact in the plane direction and an impact in one direction.

A method of manufacturing the molded article of the composite resincontaining fibers will be described below.

FIG. 4 is a flowchart showing the manufacturing process of the moldedarticle of the composite resin containing fibers according to thepresent embodiment.

At first, the base resin, and the fibrous filler are charged, and thedispersant are optionally charged into a melt-kneading device and thenare melted and kneaded in the melt-kneading device. Thus, the base resinis melted and the fibrous filler and the dispersant are dispersed intothe melted base resin; meanwhile, the shearing action of the devicefurther fibrillates agglomeration of the fibrous filler, thereby finelydispersing the fibrous filler into the base resin.

In the related art, fibrous filler are used that is obtained byfibrillating fibers beforehand by pretreatment such as wet dispersion.However, when the fibrous filler is fibrillated beforehand in a solventused for wet dispersion, the fibrillation is accelerated more than inthe molten base resin. Thus, it is difficult to fibrillate only the endsof fibrous filler, so that the fibrous filler is fully fibrillated.Moreover, the addition of the pretreatment step reduces productivity.

In contrast, in the manufacturing process of the molded article of thecomposite resin containing fibers according to the present embodiment,melting and kneading (full dry process) are performed with the baseresin and the dispersant without pretreatment including wet dispersionfor fibrillating and modifying the fibrous filler. In this process, wetdispersion is not performed on the fibrous filler and thus only the endsof the fibrous filler are fibrillated as has been discussed. Moreover,the productivity can be improved with a small number of steps.

The composite resin discharged from the melt-kneading device is formedinto a pellet shape through the cutting step using a pelletizer or thelike. Pelleting methods executed immediately after the melting of resininclude an air hot-cut method, an underwater hot-cut method, and astrand cut method. Furthermore, a pulverization method is available inwhich a molded component or a molded sheet is pulverized or cut.

The molded article of the composite resin containing fibers can beproduced by injection-molding the pellets. As has been discussed, thecomposite fibrous filler of the molded article has a structure includinga large-diameter fiber part that is not fibrillated and a small-diameterfiber part with partially fibrillated ends in the fiber lengthdirection. Thus, an impact in one direction can be received by thelarge-diameter fiber part that is not fibrillated, and the expansion ofcracking defects caused by a surface impact can be suppressed by thefibrillated small-diameter part. This can achieve the molded articlewith high impact resistance and a high modulus of elasticity.

Examples and comparative examples in experiments conducted by thepresent inventors will be described below.

Example 1

Pulp dispersion polypropylene pellets were manufactured according to amanufacturing method, which will be discussed below, and then aninjection molded article was manufactured using the pellets.

Polypropylene (Prime Polymer Co., Ltd., trade name: J108M) as a baseresin, flocculate softwood pulp (Mitsubishi Paper Mills Limited, tradename: NBKP Celgar) as a fibrous filler, and maleic anhydride (SanyoChemical Industries, Ltd., trade name: UMEX) as a dispersant wereweighted in a mass ratio of 85:15:5 and then were dryblended. Afterthat, the base resin, the fibrous filler, and the dispersant weremelted, kneaded, and dispersed by a twin-screw kneader (Kurimoto, Ltd.,S-1KRC kneader, a screw diameter: 25 mm, L/D: 10.2). A shearing forcecan be changed by modifying the screw configuration of the twin-screwkneader. In example 1, according to the specifications of a mediumshearing type, the temperature of a kneading unit was set at 180° C. andan extrusion speed was set at 0.5 kg/h. Furthermore, melting, kneading,and dispersion were repeated ten times under these conditions so as toperform treatment for an extended time. Molten resin materials werehot-cut to produce pulp dispersion polypropylene pellets.

By using the produced pulp dispersion polypropylene pellets, a moldedtest piece of a composite resin containing fibers was produced by aninjection molding machine (The Japan Steel Works, LTD., 180AD). Theproduction conditions of the test piece included a resin temperature of190° C., a mold temperature of 60° C., an injection speed of 60 mm/s,and a dwell pressure of 80 Pa. The entry of pellets charged to the screwof the molder through a hopper was measured according to a reduction inthe amount of pellets per hour. The entry was confirmed to be constant.The shapes of the molded article and the test piece were changedaccording to evaluation items, which will be discussed below, a dumbbellof size No. 1 was produced for measuring a modulus of elasticity, and aplate measuring 50 mm per side and a thickness of 1.2 mm was producedfor a weight drop impact test. The molded article was evaluated usingthe obtained test piece according to the following method:

The Median Fiber Diameter of the Non-Fibrillated Part 4 and the MedianFiber Diameter of the Fibrillated Part 3

The obtained molded article was immersed into a xylene solvent,polypropylene was melted, and then an SEM observation of remaining pulpfibers was made. Specifically, about 100 representative fibers weremeasured using an SEM (Phenom-World, scanning electron microscope PhenomG2pro). As a result of calculation of median fiber diameters frommeasurement results of fiber diameters, a non-fibrillated part had amedian fiber diameter of 5.2 µm, and fibrillated parts found on the endsof fibers in the fiber length direction had a median fiber diameter of0.7 µm.

Modulus of Elasticity

A tensile test was conducted on the obtained test piece of the No. 1dumbbell shape by a tension tester (A&D Company, Limited, RTF-1310). Inan evaluation method of a modulus of elasticity, a numeric value lowerthan the modulus of elasticity of the base resin was judged as being “nogood”, whereas a numeric value higher than the modulus of elasticity wasjudged as being “good”. The base resin had a modulus of elasticity of1.3 GPa while the test piece had a modulus of elasticity of 2.1 GPa,which is 1.62 times that of the base resin. Thus, the test piece wasjudged as being “good”.

Weight Drop Impact Test

A weight drop impact test was conducted using the obtained flat testpiece (the flat test piece made of a fiber composite resin which was cutwith a thickness of 1.2 mm). Specifically, the test piece was left atrest in a constant temperature oven (ESPEC CORP., trade name: PDR-3KP)and was kept at -10° C. for three hours. After that, the test piece wasquickly removed from the constant temperature oven, and then a maximumheight H for an unbroken test piece was measured when a weight of 250 gwas dropped from different heights. According to the weight drop impacttest, the larger the numeric value of the maximum height, the larger thesurface impact resistance of the test piece. In this case, the surfaceimpact resistance was measured as follows: if the numeric value of themaximum height for the test piece was smaller than 0.4 times the maximumheight for an unbroken base resin, the surface impact resistance wasevaluated to be “not good”, that is, a low surface impact resistance. Ifthe numeric value of the maximum height for the test piece was 0.4 to1.0 times, the surface impact resistance was evaluated to be “good”,that is, a high surface impact resistance. The maximum height Ho for anunbroken test piece only made of the base resin was 200 cm, whereas themaximum height for the test piece of Example 1 was 190 cm, which is 0.95times that of the base resin. Thus, the test piece of Example 1 wasevaluated to be “good”.

Charpy Impact Test

The obtained test piece of the No. dumbbell shape was notched beforehandand then a Charpy impact test (JIS K7111) was conducted using a tester(Toyo Seiki Seisaku-sho, Ltd., DIGITAL IMPACT TESTER). In the Charpyimpact test, the higher the impact strength, the higher the resistanceof the test piece to an impact in one direction. In a method ofevaluating resistance to an impact in one direction, if the Charpyimpact strength of the test piece was less than 0.4 times that of a testpiece only made of the base resin, the test piece was evaluated to be“no good”, that is, less resistant to an impact in one direction. If theCharpy impact strength of the test piece was 0.4 to 1.0 times, the testpiece was evaluated to be “good”, that is, highly resistant to an impactin one direction. The test piece of the base resin had a Charpy impactstrength of 7.8 kJ/m², whereas the test piece had a Charpy impactstrength of 3.3 kJ/m², which is 0.42 times that of the base resin. Thus,the test piece was evaluated to be “good”.

Example 2

Example 2 was different from example 1 in that melting, kneading, anddispersion were repeated three times, which was shorter than that ofexample 1. Other conditions were similar to those of example 1 whilepulp dispersion polypropylene pellets and a molded article as a testpiece were produced. An evaluation was carried out in the same manner asin example 1.

(Comparative Example 1)

In comparative example 1, a molded article was produced only usingpolypropylene pellets, though the screw configuration and otherconditions are similar to those of example 1. An evaluation was carriedout in the same manner as in example 1.

(Comparative Example 2)

In comparative example 2, the screw configuration as in example 1 waschanged to a high shearing type. Pulp dispersion polypropylene pelletsand a molded article were produced under the same conditions as those ofexample 1 except for the screw configuration. An evaluation was carriedout in the same manner as in example 1.

(Comparative Example 3)

In comparative example 3, a screw configuration as in example 1 waschanged to the high shearing type of comparative example 2. Moreover,the repetition of melting, kneading, and dispersion in the screwconfiguration was shortened to three times. Other conditions weresimilar to those of example 1 while pulp dispersion polypropylenepellets and a molded article were produced. An evaluation was carriedout in the same manner as in example 1.

(Comparative Example 4)

In comparative example 4, a screw configuration as in example 1 waschanged to the high shearing type of comparative example 2. Moreover,the repetition of melting, kneading, and dispersion in the screwconfiguration was shortened to a single time. Other conditions weresimilar to those of example 1 while pulp dispersion polypropylenepellets and a molded article were produced. An evaluation was carriedout in the same manner as in example 1.

(Comparative Example 5)

In comparative example 5, a screw configuration as in example 1 waschanged to a low shearing type. Other conditions were similar to thoseof example 1 except for the screw configuration while pulp dispersionpolypropylene pellets and a molded article were produced. An evaluationwas carried out in the same manner as in example 1.

(Comparative Example 6)

In comparative example 6, flocculate softwood pulp serving as thefibrous filler of example 1 was changed to commercially available glassfibers. Other conditions were similar to those of example 1 except forthe type of fibrous filler while pulp dispersion polypropylene pelletsand a molded article were produced. An evaluation was carried out in thesame manner as in example 1.

Table 1 shows the measurement results of examples 1 and 2 andcomparative examples 1 to 6.

TABLE 1 Fibrous filler Molded article Type Amount of addition Medianfiber diameter of a non-fibrillated part Median fiber diameter of afibrillated part Modulus of elasticity Maximum height of a weight dropimpact test Impact strength of a Charpy impact test Measured value RatioEvaluation Measured value Ratio Evaluation Measured value RatioEvaluation Example 1 Cellulose (conifer) 15 mass% 5.2 µm 0.7 µm 2.1 GPa1.62 Good 190 cm 0.95 Good 3.3 kJ/m² 0.42 Good Example 2 Cellulose(conifer) 15 mass% 28.1 µm 1.8 µm 1.7 GPa 1.32 Good 85 cm 0.43 Good 7.4kJ/m² 0.95 Good Comparative example 1 None 0 mass% – – 1.3 GPa 1(Reference) – 200 cm 1 (Reference) – 7.8 kJ/m² 1 (Reference) –Comparative example 2 Cellulose (conifer) 15 mass% 0.9 µm 0.07 µm 1.4GPa 1.08 Good 10 cm 0.05 No good 1.7 kJ/m² 0.22 No good Comparativeexample 3 Cellulose (conifer) 15 mass% 4.1 µm 0.8 µm 1.6 GPa 1.23 Good160 cm 0.80 Good 2.2 kJ/m² 0.28 No good Comparative example 4 Cellulose(conifer) 15 mass% 35.0 µm 1.0 µm 1.7 GPa 1.32 Good 15 cm 0.08 No good2.8 kJ/m² 0.36 No good Comparative example 5 Cellulose (conifer) 15mass% 25.2 µm 2.2 µm 1.6 GPa 1.23 Good 70 cm 0.35 No good 6.5 kJ/m² 0.83Good Comparative example 6 Glass fibers 15 mass% 29.8 µm – 3.1 GPa 2.38Good 10 cm 0.05 No good 13.0 kJ/m² 1.67 No good

As is evident from Table 1, as compared with the modulus of elasticityof the base resin not containing the fibrous filler in comparativeexample 1, the test pieces containing the fibrous filler in otherexamples and comparative examples had higher moduli of elasticity andhigher mechanical strength. It was confirmed that a surface impactstrength measured in the weight drop impact test in examples 1 and 2 was0.4 to 1.0 times that of comparative example 1. In examples 1 and 2, thefibrous filler was added, the non-fibrillated part had a median fiberdiameter of 5 to 30 µm, and the fibrillated part had a median fiberdiameter of 0.1 to 2 µm. Moreover, in examples 1 and 2, an impactstrength in the surface impact strength in the weight drop impact testwas 0.4 to 1.0 times that of comparative example 1 and an impactstrength in one direction in the Charpy impact test was 0.4 to 1.0 timesthat of comparative example 1. Thus, it was confirmed that impactresistance was ensured in a normal use environment.

In contrast, in comparative example 2 where the screw configuration waschanged to the high shearing type, excessive shearing reduced the medianfiber diameter of a fibrillated part to 0.07 µm and the median fiberdiameter of a non-fibrillated part to 0.9 µm. The fiber length alsoreduced to extremely short. This reduced a fiber aspect ratio (an indexexpressed by “a fiber length divided by a fiber diameter”). Hence, thesurface impact strength and the impact strength in one direction werelower than 0.4 times that of comparative example 1, so that impactresistance was not ensured in a normal use environment.

In comparative example 3 where the screw configuration was changed tothe high shearing type as in comparative example 2 and the repetition ofmelting, kneading, and dispersion was reduced to three times to shortentreatment, a fibrillated part had a median fiber diameter of 0.8 µm. Inother words, it was confirmed that fine fibrillation ensured impactresistance in a normal use environment when a surface impact wasapplied. However, a non-fibrillated part had an extremely small medianfiber diameter of 4.1 µm. Hence, the expansion of cracking defects wasnot suppressed against an impact strength in one direction. The impactstrength was lower than 0.4 times that of comparative example 1, so thatimpact resistance was not ensured in a normal use environment.

In comparative example 4 where the number of times of melting, kneading,and dispersion was further reduced to one from the conditions ofcomparative example 3 to shorten treatment, a non-fibrillated part(including an insufficiently fibrillated part) had a large median fiberdiameter of 35.0 µm. Thus, even in the presence of sufficientlyfibrillated parts, large crazing defects occurred near non-fibrillatedparts from the time when molded. Furthermore, crazing defects werelikely to be connected to one another by an impact force both in theplane direction and one direction. This increased the occurrence ofcracking from the crazing defects. Thus, a surface impact strength andan impact strength in one direction were lower than 0.4 times that ofcomparative example 1, so that impact resistance was not ensured in anormal use environment.

In comparative example 5 where the screw configuration was changed tothe low shearing type, a non-fibrillated part had a small median fiberdiameter of 25.2 µm. However, low shearing causes insufficientfibrillation such that a fibrillated part had a median fiber diameter of2.2 µm. Thus, crazing defects on the ends of fibrillated parts arelikely to be connected to one another. This reduced the surface impactstrength to less than 0.4 times that of comparative example 1, so thatimpact resistance was not ensured in a normal use environment.

In comparative example 6 where the fibrous filler was changed to glassfibers, glass had a modulus of elasticity of 68 GPa, which is quitehigher than 1.5 GPa, the modulus of elasticity of polypropylene in thebase resin. Thus, resistance to an impact in one direction had a highervalue than that of comparative example 1 but strong anisotropy in afiber direction caused a surface impact strength in multiple directionsto be lower than 0.4 times that of comparative example 1. In the case ofglass fibers, the ends of the fibrous filler do not have distinctfibrillated parts. Thus, a number of large crazing defects occurred nearthe fibers of non-fibrillated parts and were likely to be connected toone another, leading to a lower surface impact strength than that ofcomparative example 1.

According to the evaluations, in the fibrous filler added to the moldedarticle, each fiber has a large-diameter fiber part that is notfibrillated and small-diameter fiber parts with partially fibrillatedends in the fiber length direction. This allows the non-fibrillatedlarge-diameter fiber part to receive an impact in one direction and thefibrillated small-diameter fiber part to suppress the expansion ofcracking defects caused by a surface impact, thereby providing a moldedarticle with a surface impact strength and an impact strength in onedirection.

The present invention can improve the characteristics of the base resinand thus can be an alternative of engineering plastics or metallicmaterials. This can remarkably reduce the manufacturing cost ofindustrial products made of engineering plastics or metals or articlesfor daily use. The present invention is also applicable to the cabinetsof household appliances, building materials, and automobile parts.

What is claimed is:
 1. A molded article of a composite resin containingfibers, the composite resin containing a fibrous filler in base resin,wherein the fibrous filler has a fibrillated part on each end of thefibrous filler in a fiber length direction, the composite resin exhibitsphysical characteristics satisfying: Ho × 0.4 ≤ H ≤ Ho where H is amaximum height when a first plate-like test piece is not broken when aweight of 250 g is dropped from a certain height after the firstplate-like test piece is kept at -10° C. for three hours, the firstplate-like test piece being made of the composite resin with a thicknessof 1 to 2 mm; and Ho is a maximum height when a second plate-like testpiece is not broken when a weight of 250 g is dropped from a certainheight after the second plate-like test piece is kept at -10° C. forthree hours, the second plate-like test piece being only made of thebase resin with the same thickness as the first plate-like test piece,and So × 0.4 ≤ S ≤ So where S is a Charpy impact strength specified inJIS K 7111 of the molded article of the composite resin, and So is aCharpy impact strength specified in JIS K 7111 of the molded articleonly made of the base resin.
 2. A molded article of a composite resincontaining fibers, the composite resin containing a fibrous filler inbase resin, wherein the fibrous filler has a non-fibrillated part thatis not fibrillated and a fibrillated part on each end of the fibrousfiller in a fiber length direction.
 3. The molded article of thecomposite resin containing fibers according to claim 2, wherein thefibrous filler has a median fiber diameter of 0.1 to 2 µm on thefibrillated part, and the fibrous filler has a median fiber diameter of5 to 30 µm on the non-fibrillated part.
 4. The molded article of thecomposite resin containing fibers according to claim 1, wherein thefibrous filler is natural fibers of cellulose.
 5. The molded article ofthe composite resin containing fibers according to claim 1, wherein thebase resin is an olefin resin.
 6. A molded article of a composite resincontaining fibers, the composite resin containing a fibrous filler inbase resin, wherein the fibrous filler has a non-fibrillated part thatis not fibrillated at the center of the fiber in a fiber lengthdirection and a fibrillated part on each end of the fibrous filler inthe fiber length direction, the fibrous filler has a median fiberdiameter of 0.1 to 2 µm on the fibrillated part and has a median fiberdiameter of 5 to 30 µm on the non-fibrillated part, the fibrillated partprevents cracking caused by connection of a plurality of crazing defectsoccurring when an impact force is applied to the molded article in aplane direction, and the non-fibrillated part that is not fibrillatedprevents cracking defects occurring when an impact force is applied tothe molded article in one direction as in a Charpy impact test.